Why does my network have such a small percentage of use?

Note: this could be a violation of Rule #1, but it's more of a general use question.

I'm uploading a pretty large file to YouTube (30GB of 1080p 60fps footage, 2hrs), and I'm getting anywhere from 6.0 to 6.2 Mbps, but Task Manager says that I am only at 4% utilization. I guess my question is, why is it that it uses such a small percentage when it could easily use more (No one else is using my internet ATM), and just expedite my video's upload? Is there a workaround for this that would make my internet faster? Is there a limit that my provider puts on it?

Thanks!